package com.juc.concurrency.jucExample.atomic;

import com.juc.concurrency.annoations.ThreadSafe;
import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;
import java.util.concurrent.atomic.AtomicLong;

/**
 * 原子类之 AtomicLong
 * 我们知道，AtomicLong是利用了底层的CAS操作来提供并发性的，比如addAndGet方法
 * addAndGet方法调用了Unsafe类的getAndAddLong方法，该方法是个native方法，它的逻辑是采用自旋的方式不断更新目标值，直到更新成功。
 * 在并发量较低的环境下，线程冲突的概率比较小，自旋的次数不会很多。但是，高并发环境下，N个线程同时进行自旋操作，会出现大量失败并不断自旋的情况，此时AtomicLong的自旋会成为瓶颈
 */
@Slf4j
@ThreadSafe
public class AtomicLongExample2 {

    // 请求总数
    public static int clientTotal = 5000;

    // 同时并发执行的线程数
    public static int threadTotal = 200;

    public static AtomicLong count = new AtomicLong(0);

    public static void main(String[] args) throws Exception {
        ExecutorService executorService = Executors.newCachedThreadPool();
        final Semaphore semaphore = new Semaphore(threadTotal);
        final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
        for (int i = 0; i < clientTotal; i++) {
            executorService.execute(() -> {
                try {
                    semaphore.acquire();
                    add();
                    semaphore.release();
                } catch (Exception e) {
                    log.error("exception", e);
                }
                countDownLatch.countDown();
            });
        }
        countDownLatch.await();
        executorService.shutdown();
        log.info("count:{}", count.get());
    }

    private static void add() {
        count.incrementAndGet();
        // count.getAndIncrement();
    }
}
